A constituent component of interest in a solid or liquid sample may be extracted by use of laboratory-based techniques known in the sample preparation arts. One useful extraction process is solvation, whereby application of a solvent fluid to the sample causes constituent components to be dissolved in the solvent. The constituent component of interest in such an extraction process may be either the isolated material (known as the extract) or the material remaining in the sample after extraction (known as the raffinate). Another process of extraction may be achieved by volatilization, wherein the constituent components of interest are swept or otherwise released from the sample by the influence of a vapor pressure differential.
However, the aforementioned extraction processes heretofore have been difficult to perform in a simple, manually-operable instrument that is suited for use not only in the laboratory, but more importantly, in a location outside of the laboratory. Such an instrument would be considered field-portable and would be useful outside of the laboratory for performing remote sample analysis or field monitoring.
A need also exists to simplify the aforementioned extraction processes, regardless of whether they may be employed in the field or in the laboratory, because conventional extraction procedures are expensive, labor-intensive, equipment-intensive, and time-consuming. In particular, it would be highly desirable for effecting a volatilization process in a field-portable extraction instrument so as to obtain an extract or raffinate in a form that is quickly and easily introduced into a field-portable analytical instrument. Alternatively, there is a need for providing such extraction in the field whereby the extract or raffinate is produced in a container or vessel that is easily transportable to an analytical instrument that is not portable and which may be situated nearby, such as in a vehicle, or at a location quite distant from the monitored site, such as in a laboratory.
A field-portable extraction system that employs an extraction fluid in the form of a solvent fluid at a an elevated pressure (i.e., above atmospheric pressure) is also desirable. For example, supercritical fluids have been used as solvents in extraction instruments. When compared to typical liquid solvents, the supercritical fluid has particular transport properties that allow enhanced mass transport within complex sample matrices, such as coal, plant tissue, or animal tissue. These attributes make supercritical fluids especially attractive for performing sample extraction in the field. However, the requisite pressure is conventionally achieved by use of high-pressure pumps and related apparatus that are typically not suited for portable use. This problem is especially difficult in constructing extraction systems that operate with solvent fluids at supercritical conditions, as well as in extraction systems that use solvent fluids at near-critical conditions.
It would be desirable and of considerable advantage to provide a sample extraction technique that differs from that employed in the traditional laboratory-based extraction, so as to be effective in the field, even if such a new technique provides less-than-perfect extraction.